Method to improve the brightness of zinc from an alkaline zincate electrodeposition bath

ABSTRACT

1. AN AQUEOUS ALKALINE ELECTROPLATING BATH COMPRISING INC OXIDE, ALKALI METAL HYDROXIDE, POLYETHYLENEIMINE HAVING A MOLECULAR WEIGHT OF FROM 1,000 TO 400,000 AND BEING PRESENT IN A CONCENTRATION OF 0.2 TO 100 GRAMS PER LITER AND A ZINC BRIGHTENING AMOUNT OF A NITROGEN HETEROCYCLIC COMPOUND OF THE FORMULA:   X&lt;(-A=N OR -N(-R3)N-C(-R2)=C(-R1)-)   WHEREIN X IS   -S- OR &gt;N-R3, AND   A IS INDEPENDENTLY SELECTED FROM THE GROUP CONSISTING OF   &gt;C-N(-R3)2; &gt;C=S; -C(=S)-R3; &gt;C=N-R3 AND &gt;CH2   N IS O OR 1; WHEN N IS 0, NITROGEN IS DOUBLY BONDED TO CARBON IN A; WITH THE PROVISO THAT WHEN N IS O, A IS   &gt;C-N(-R3)2; &gt;C-S(R)3 OR &gt;CH2   R1 AND R2 ARE INDEPENDENTLY SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALKYL OF 1 TO 4 CARBONS, PHENYL; AND MAY BE JOINED TO FORM A SIX MEMBERED AROMATIC CARBOCYCLIC RING WHICH MAY BE SUBSTITUTED AND R3 IS HYDROGEN, ALKYL OF 1 TO 4 CARBON ATOMS OR PHENYL.

United States Patent Office Patented Oct. 15, 1974 3,841,982 METHOD TOIMPROVE THE BRIGHTNESS OF ZINC FROM AN ALKALINE ZINCATE ELEC- US. Cl.204-55 R 36 Claims ABSTRACT OF THE DISCLOSURE An aqueous alkalineelectroplating bath comprising zinc oxide, alkali metal hydroxide,polyethyleneimine and a zinc brightening amount of a nitrogenheterocyclic compound of the formula:

wherein X is S- or A is independently selected from the group consistingn is or 1; when n is 0, nitrogen is doubly bonded to carbon in A; withthe proviso that when n is 0, A is R and R are independently selectedfrom the group consisting of hydrogen, alkyl of l to 4 carbon atoms,phenyl; and may be joined to form a six membered aromatic carbocyclicring and R is hydrogen, alkyl of 1 to 4 carbon atoms or phenyl.

CROSS REFERENCE TO RELATED CASES This case is a continuation-in-part ofUS. Ser. No. 244,938, filed Apr. 17, 1972, now abandoned.

BACKGROUND OF THE INVENTION Zincate plating baths have been used as ameans of electrodepositing zinc without employing cyanide ions due tothe difficulty in disposing of cyanide ions in waste efiluent.Previously, it had been difficult to electrodeposit a bright zincdeposit from a zincate bath over a wide current density area. Someconventional zinc brighteners produce a bright deposit but only over anarrow current density range. The high current density areas generallyresulted in a spongy or burnt deposit. It has been found through thecombination of brighteners employed in the present case to obtain notonly a bright deposit, but also a deposit over a wide current densityarea.

It has also been found that with conventional brigheners relative largeamounts are required to obtain brightness while with the components ofthe present invention relatively less amounts are needed to obtain abright deposit.

Some zinc brighteners have been described in US. 3,296,105; US.3,317,412; US. 3,393,135; US. 3,472,743 and German 1,232,800.

SUMMARY OF THE INVENTION A method is described for obtaining a brightzinc electrodeposit over a wide current density area from a zincateelectroplating bath by employing a combination of additives, the firstbeing a polyethyleneimine and the second one being a heterocyclicnitrogen containing compound.

DESCRIPTION OF PREFERRED EMBODIMENTS A method is described for obtaininga bright zinc deposit from an alkaline bathpreferably a cyanide freealkaline zincate bath wherein the bath contains polyethyleneimine and abrightening amount of a nitrogen heterocyclic compound of the structure:

wherein X is S or I NR,; and

A is independently selected from the group consisting n is 0 or 1; whenn is 0, nitrogen is doubly bonded to carbon in A; with the proviso thatwhen n is 0, A is R and R are independently selected from the groupconsisting of hydrogen, alkyl of 1 to 4 carbon atoms, phenyl; and may bejoined to form a six membered aromatic carbocyclic ring and R ishydrogen, alkyl of 1 to 4 carbon atoms or phenyl.

Zincate plating baths are those which generally contain zinc oxide andcaustic, such as sodium hydroxide. The amount of sodium hydroxide thatmay be employed ranges from 50 to 250 grams/liter, preferably from aboutto about 200 grams/liter, while the amount of zinc oxide ranges from 5to 50 grams/liter, preferably from about 8 to about 30 grams/liter.

The processing parameters are such that normally atmospheric temperatureand pressure is employed, although temperatures up to 55 C. may also beemployed, and even more preferably 15 to about 45 C. The cathode currentdensity ranges from about 5 to 25 amps per sq. ft. while the anodecurrent density ranges from about 10 to 35 amps per sq. ft. where thezinc deposition can occur with agitation.

Other agents may also be present in the bath, such as those described inthe above patents. Examples of such suitable agents may be anisaldehyde,glue, polyvinyl alcohol and the glycerol ester of polyvinyl alcoholwherein these alcohols have a molecular weight of 5,000 to 20.- 000.Other polymers that may be employed are gelatin, peptone, and the like.In addition, chelating agents or agents which can form a complex withthe metal zinc in the bath may also be employed, such asnitrilotriacetic acid and the various alkali metal salts, such as thesodium salt, ethylenediaminetetraacetic acid, and its water solublesalts, such as sodium, and the like.

The polyethyleneimine that may be used in the present case has amolecular weight ranging from 1,000 to 400,- 000, preferably 600 to60,000 where the percentage of primary, secondary and tertiary nitrogenatoms is about 25, 50, and 25% respectively.

A zincate bath that may be employed in the present invention is asfollows:

The bath pH may be adjusted by adding NaOl-I. Some of the nitrogenheterocylic compounds that may be employed in the present invention areas follows.

TNH; s H N N n N s T511 K TNH: H N

' l uHs s =s /N HZN j Tsn s s -sH -s-on3 n l HzN H l CH3 CH3 \FNH momHzN If 1? H H n N N Ts-orn H H-sn nm N N E N S S H S H 71 1 HzN -N N mB4 --N wherein R is a water solubilizing group.

By water solubilizing group is meant any substituent on the six memberedcarbocyclic ring which will improve the water solubility of thecompound. Such groups are hydroxy, alkoxy, such as methoxy or ethoxy andthe like, carboxy, amino, and the like. In addition, R may be othergroups which are not detrimental to the electrodeposition of zinc suchas chloro, bromo, cyano (CN), nitro and the like.

EXAMPLE 1 A zincate plating bath was formulated containing the followingcomponents and was used to electrodeposit zinc onto a steel substrate ata cathode current density of ASP and a temperature of 75 F.

Sodium hydroxide 140 grams/liter; zinc oxide -12 grams/liter;polyethyleneimine (1,200 molecular weight) 2 grams/liter,nitrilotriacetic acid trisodium salt 1 gram/ liter; andZ-amino-benzothiazole 0.03 grams/liter.

After plating rod like structures in a typical barrel plating apparatusfor 25-30 minutes a uniform bright zinc deposit of 0.2-0.3 mil thicknesswas obtained. The initial bath pH is about 14.

EXAMPLE 2 Zincate plating bath similar to the above was also preparedbut further including 0.1 g./l. of polyvinyl alcohol. A bright zincdeposit was obtained over a broad current density range following theprocedure of Example #1.

EXAMPLE 3 The procedure of Example #1 was followed, except that the bathalso contained 0.1 grams/liter of anisaldehyde with equivalent resultsbeing obtained.

EXAMPLE 4 The procedure of Example #1 was followed, except that the bathalso contained 0.1 grams/liter of anisaldehyde and 0.1 grams/liter ofpolyvinyl alcohol with equivalent results being obtained.

EXAMPLE 5 A cyanide free alkaline zincate bath was formulated asfollows:

G./l. NaOH 140 ZnO 15 Z-mercaptobenzothiazole 0.03 polyethyleneimine(1200 molecular wt.) 3

Following the procedure of Example #1 equivalently good results wereobtained.

What is claimed is:

1. An aqueous alkaline electroplating bath comprising inc oxide, alkalimetal hydroxide, polyethyleneimine having a molecular weight of from1,000 to 400,000 and being present in a concentration of 0.2 to gramsper liter and a zinc brightening amount of a nitrogen heterocycliccompound of the formula:

i 3)n wherein X is -S- or I!\IR3; and

A is independently selected from the group consisting of 11 is 0 or 1;when n is 0, nitrogen is doubly bonded to carbon in A; with the provisothat when n is O, A is R and R are independently selected from the groupconsisting of hydrogen, alkyl of 1 to 4 carbons, phenyl; and may bejoined to form a six membered aromatic carbocyclic ring which may besubstituted and R is hydrogen, alkyl of 1 to 4 carbon atoms or phenyl.

2. The bath of Claim 1 wherein R and R are joined to form a six memberedaromatic carbocyclic ring.

3. The bath of Claim 2 wherein the carbocyclic ring is substituted by anamino group.

4. The bath of Claim 2 wherein the carbocyclic ring is substituted by abath solubilizing group.

5. The bath of Claim 1 wherein the nitrogen heterocyclic compound ispresent in an amount ranging from about 0.005 to about 5 grams/ liter.

6. The bath of Claim 1 wherein X is S.

7. The bath of Claim 1 wherein X is -I IRa.

'8. The bath of Claim 1 wherein A is 9. The bath of Claim 1 wherein A is10. The bath of Claim 1 wherein A is 11. The bath of Claim 1 wherein Ais 12. The bath of Claim 1 wherein n is 0.

13. The bath of Claim 1 wherein R is hydrogen.

1-4. The bath of Claim 1 wherein R and R are hydrogen.

15. The bath of Claim 1 wherein the nitrogen heterocyclic compound isaminobenzothiazole.

16. The bath of Claim 1 wherein the nitrogen heterocyclic compound is anamino-2-mercaptobenzothiazole.

17. The bath of Claim 1 wherein the nitrogen heterocyclic compound is2-imino, 3-a1kyl benzothiazole.

18. A method of depositing bright zinc from a zincate electroplatingbath comprising electrolyzing the bath of Claim 1 for a period of timesuflicient to form a bright zinc deposit onto a cathodic surface.

19. The method of Claim 18 wherein R and R are joined to form a sixmembered aromatic carbocyclic ring.

20. The method of Claim 19 wherein the carbocyclic ring is substitutedby an amino group.

21. The method of Claim 19 wherein the carbocyclic ring is substitutedby a bath solubilizing group.

22. The method of Claim 18 wherein the nitrogen heterocyclic compound ispresent in an amount ranging from about 0.005 to about 5 grams/ liter.

23. The method of Claim 18 wherein X is S.

24. The method of Claim 18 wherein X is ALB.

'25. The method of Claim 18 wherein A is J a)z- 26. The method of Claim18 wherein A is 27. The method of Claim 18 wherein A is -.iJ-s (R3). 28.The method of Claim 18 wherein A is 29. The method of Claim 18 wherein nis 0.

30. The method of Claim 18 wherein R is hydrogen.

31. The method of Claim 18 wherein R and R are hydrogen.

32. The method of Claim 18 wherein the nitrogen heterocyclic compound isaminobenzothiazole.

33. The method of Claim 18 wherein the nitrogen heterocyclic compound isan amino2-mercaptobenzothiazole.

34. The method of Claim 18 wherein the nitrogen heterocyclic compound is2-imino, 3'alkyl benzothiazole.

35. The method of Claim 18 wherein the cathodic surface is metallic.

36. A cyanide free alkaline zincate electroplating bath comprising zincoxide, alkali metal hydroxide, polyethyleneimine having a molecularweight of from 1,000 to 400,000 and being present in a concentrationfrom 0.2 to 100 grams per liter and a zinc brightening amount of anitrogen heterocyclic compound of the formula:

wherein X is S- or l lR and A is independently selected from the groupconsisting of n is O or 1; when n is 0, nitrogen is doubly bonded tocarbon in A; with the proviso that when n is 0, A is R and R areindependently selected from the group consisting of hydrogen, alkyl of 1to 4 carbon atoms, phenyl; and may be joined to form a six memberedaromatic carbocyclic ring which may be substituted and R is hydrogen,alkyl of 1 to 4 carbon atoms or phenyl.

References Cited UNITED STATES PATENTS 2,853,444 9/1958 Pye et a1 204- RX 2,892,760 6/1959 Giindel et a1 204-44 3,267,010 8/ 1966 Creutz et a120452 R 3,672,971 6/1972 Senge et al. 204-55 R 3,723,263 3/ 1973Rosenberg 204-55 R FOREIGN PATENTS 1,243,488 6/1967 Germany 204-55 R1,263,445 3/ 196 8 Germany 20455 R a GERALD L. KAPLAN, Primary Examiner

1. AN AQUEOUS ALKALINE ELECTROPLATING BATH COMPRISING INC OXIDE, ALKALIMETAL HYDROXIDE, POLYETHYLENEIMINE HAVING A MOLECULAR WEIGHT OF FROM1,000 TO 400,000 AND BEING PRESENT IN A CONCENTRATION OF 0.2 TO 100GRAMS PER LITER AND A ZINC BRIGHTENING AMOUNT OF A NITROGEN HETEROCYCLICCOMPOUND OF THE FORMULA: